Do cinder blocks leach anything?

[mathman]

I would like to use a couple "bricks" (cinder blocks) to prop up my live rock. Is this safe? Should I take a precautions?

[Reef Bass]

I know the use of cinder blocks in contact with the water of koi ponds is bad. Something about the block leaching and driving the ph through the proverbial roof.

I have heard of people soaking and bathing their cinder blocks in vinegar to attempt to neutralize it. There are also critter safe paints that can be applied to seal it.

I would not stick a "raw" cinder block in my koi pond or reef tank.

I have heard of people using bricks in their ponds without ill effects, but I'm not recommending sticking a brick in your reef tank either.

[mathman]

I have several cinder blocks in my pond to prop up my lillies. I think the pH rise would dissipate after 24 hrs or so; so just don't add more than one at a time.

Are cinder blocks made with silica? Would this leach out?

[Dz99ls]

i agree dont use plus this will add alot of weight if you need a prop of some kind hyst make some kind of pvc frame

[Randy Holmes-Farley]

I expect that most things we call cinder blocks are largely some sort of concrete these days, but I am not certain (anyone know for sure?). They can leach things the might raise pH and might also release impurities. Rinsing it well, maybe even with a quick vinegar rinse would be beneficial. I do know that many folks have used them, but I am uncertain exactly how they treated them, or if the compositions vary enough to have some be problematic while others are not.

[Valab]

Concrete ('cinder') blocks dump hydroxide when wet. This can happen for a few days or for months after they're submerged. There is no way to calculate ahead of time how much a given block will actually release. The 'problem' is worse with freshwater tanks (ponds) since they usually don't have the buffering capacity of salt tanks. I put two of the larger blocks (LXWXH = 12X6X6) in my system (400 gal) and it didn't change the pH at all. There are tons of folks who have used these as 'base rock' in really large tanks without apparent ill effects, so I say go for it.

[Hobster]

I think it would be much like arragocrete (sp?) I and others have made and used a lot of it. The portland cement is what raises your pH and takes a long time to cure. The other part of the mixture would be the sand which may have regional differences. You may want to soak a block in a bucket of water and test before and after a few days to see if the pH changes. maybe test for phosphates. It depends on how old or cured your blocks are. If still unsure, maybe try a cut down "milk crate" or pvc as Dz suggested.:)

[mathman]

thanks for all of your replies

[Randy Holmes-Farley]

You're welcome.

Happy Reefing. :)

[sparkey65]

i would only use a pvc frame its strong will not add any more unneaded weight to your tank